According to a working group of W-CDMA (Wideband-Code Division Multiple Access) which is known as a third-generation mobile telephone communication system, a standard is established in June of 2007, and LTE (Long Term Evolution), namely, Super3G service is scheduled to be introduced from 2009 at the earliest. This Super3G service proposes a technique that other communication system having good frequency utilizing efficiency (such as OFDM: Orthogonal Frequency Division Multiplexing) is also mixed in the same frequency band (for example, 2 GHz band), in addition to the present W-CDMA system.
However, a technique of allowing each transmission signal of a plurality of communication systems to coexist within the same frequency band, as is indicated in the description, “10.Possibility for simplified co-existence between operators in adjacent bands as well as cross-border co-existence” of the non-patent document 1 as described below, involves a problem.
Note that as is described in “11.1.1 Downlink bandwidth capabilities” of the non-patent document 2 as described below, it is agreed that in the Super3G service, a reception frequency width of mobile equipment, being a wireless communication device, is at least 10 MHz.
Non-patent document 1: TSG-RAN WGs Meeting on UTRA UTRAN LT evolution REV-05047 Tokyo, Mar. 7 and 8, 2005
Non-patent document 2: TSG-RAN WG1#44 R1-060733 Denver, Colo., USA, Feb. 13-17, 2006
In a conventional communication system, for example in the W-CDMA, a maximum frequency width of a signal in 2 GHz band is set at 20 MHz. Therefore, in 2009 when the Super3G service is scheduled to be introduced, it is necessary to achieve coexistence of signals of different communication systems within the maximum frequency band, by reducing a use band of a W-CDMA signal within 20 MHz, being the maximum frequency width, and inserting a signal of other communication system (such as an OFDM signal) into this reduced band.
Incidentally, according to the conventional W-CDMA wireless communication device, isolation between wireless communication systems is achieved by using a BPF (Band-pass filter) through which the signal of the maximum frequency width (namely 20 MHz) which is allowable in this wireless communication system is passed, or by using indexes such as an Adjacent Channel Leakage power Ratio:ACLR and an Adjacent Channel Selectivity:ACS.
Here, even in a case where a bandwidth of a signal (such as an OFDM signal) of other communication system introduced in the LTE is set at, for example 5 MHz, the reception frequency width of the mobile equipment, being the wireless communication device, is set to be at least 10 MHz in the Super3G service, as described above. Therefore, when the bandwidth of the signal of other communication system is set at 5 MHz, there is a problem of an interference of the adjacent W-CDMA signal of 5 MHz in the aforementioned 10 MHz. Namely, when a plurality of transmission signals of different communication systems exist within the same frequency band, there is a problem of interference in some cases.
Also, by future introduction of LTE, when the ratio of W-CDMA within the maximum frequency width is reduced, and a plurality of transmission signals of other communication systems (such as OFDM) having good frequency utilizing efficiency exist within the maximum frequency width, there is also a possibility of interference of the transmission signals of the same communication systems.